Glow discharge plasmas have long been used for cleaning semiconductor wafers. Various configurations of magnets are often used to trap electrons in the plasma thereby enhancing the efficiency of the device and minimizing the damage to the semiconductor due to electron bombardment. As the size of production semiconductor wafers has increased, it has been necessary to redesign the etching apparatus. Lessons learned for etching small wafers, unfortunately, do not apply for apparatus for larger wafers since the dark spaces inherent in the plasma do not scale in proportion to increased size. Each increase in the size of the wafer necessitates new research into the optimum apparatus configuration for that size.